NSA whistleblower Edward Snowden has said “circumstantial evidence and conventional wisdom” indicates that Russia is behind a major hack on the National Security Agency.

A group calling itself Shadow Brokers claimed earlier this week to have hacked the NSA and stolen cyber weapons, which it plans to sell to the highest online bidder. Very little is known about the group and security experts have said it is either a genuine hack or a very well researched hoax.

Former NSA contractor Snowden gave credence to the hack in a series of tweets on Tuesday, August 17, going as far as to suggest that the attack on the the U.S. intelligence agency’s malware server was state-backed.

“This leak is likely a warning that someone can prove U.S. responsibility for any attacks that originated from this malware server,” Snowden said. “That could have significant foreign policy consequences. Particularly if any of those operations targeted U.S. allies.”

Snowden also notes that foreign policy implications would also be significant if the U.S. operations had targeted elections, and suggested that the attack on the NSA could be an effort to influence decision-makers tasked with responding to the recent hack of Democratic National Committee (DNC) computers.

Snowden concluded: “This leak looks like somebody sending a message that an escalation in the attribution game could get messy fast.”

“We know that they arranged for a lot of those emails to be released, and we know that [Republican candidate] Donald Trump has shown a very troubling willingness to back up Putin, to support Putin,” Clinton told Fox News in the wake of the leak. “Laying out the facts raises serious issues about Russian interference in our elections, in our democracy.”